The present invention relates generally to electronic fuel injection systems for internal combustion engines in automotive vehicles and, more particularly, to a method of feedback control for an electronic fuel injection system in an internal combustion engine for an automotive vehicle.
Modern automotive vehicles have an exhaust system which includes a three-way catalyst to simultaneously reduce HC, CO and NOx emissions from an internal combustion engine in the vehicle if the fuel/air ratio of the feed gas to the engine is maintained within a narrow window. To accomplish this, automotive vehicles have used an O2 sensor located upstream of the catalyst for fuel/air feedback control.
With the current 02 sensor for feedback control, a voltage output signal of the O2 sensor is compared to a calibratible voltage threshold to determine if the fuel/air ratio is rich or lean. When the voltage output signal is determined to switch from lean to rich (for example, to go from below to above the O2 sensor switch point calibration), an O2 controller kicks lean and begins to ramp lean until the O2 sensor voltage output signal changes from rich to lean. Then, the O2 controller kicks rich and begins to ramp rich until the O2 sensor voltage output signal changes again from lean to rich.
While the use of the current O2 sensor has worked well, the O2 sensor is subject to both short and long term errors that affect fuel/air control. The short term errors are due to shifts in the O2 sensor voltage output signal based on exhaust gas temperature and composition. The long term errors are due to aging of the sensor as a result of sustained high exhaust gas temperatures and to potentially poisonous exhaust emissions. These factors can lead to a slowed O2 sensor response and a shift in the voltage of the output signal relative to the fuel/air ratio with time.
It is, therefore, one object of the present invention to provide an upstream fuel/air sensor and a downstream O2 sensor for fuel/air feedback control to improve catalyst efficiency and reduce exhaust emissions.
It is another object of the present invention to provide a method of electronic fuel injection feedback control based on the use of a fuel/air sensor upstream of the catalyst and an O2 sensor downstream of the catalyst. (Although the primary object of the present invention is exploiting the use of an upstream fuel/air sensor, the scope of the invention can also include other sensors such as a typical upstream oxygen sensor.)
To achieve the foregoing objects, the present invention provides a method of determining a goal voltage for a fuel/air sensor of an engine control system comprising the steps of determining an optimal fuel/air ratio for the current vehicle operating conditions; determining a fuel/air sensor target voltage corresponding with said optimal fuel/air ratio; applying a wave form forcing function to said fuel/air sensor voltage for providing a goal fuel/air sensor voltage having a wave form pattern; and controlling said engine to operate according to said goal fuel/air sensor voltage.
In order to obtain a high level of catalyst efficiency through the fuel/air control via a fuel/air sensor, a wave form pattern goal voltage is utilized according to the present invention. Catalysts require fuel/air perturbations to retain proper oxygen storage to maintain high efficiency. Fuel/air sensor output signals are relatively flat as opposed to the characteristics of an oxygen sensor signal, which is normally vertical at stoichiometric. Thus, a swing through the stoichiometric fuel/air mixture level becomes more difficult with a fuel/air sensor when locking on to a goal voltage. The use of a wave form pattern goal voltage insures that there are periodic fuel/air perturbations to apply a forcing function to cause the fuel/air ratio to go from rich to lean periodically.
The wave form forcing function can be a sine wave, a square wave, or V wave, or other wave forms.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.